Interrelated studies will be carried out to define what integrated factors regulate the biosynthesis of both unsaturated fatty acids and phospholipids. Prolonged feeding studies of three to four weeks, with diets containing single pure dietary lipids, will be carrid out to determine how dietary fat modification regulates the microsomal chain elongation of fatty acids. The fatty acid composition of several specific tissue lipids will also be measured to define how dietary fat modification alters the fatty acid composition of tissue lipids which serve as donors of acids which are then converted to prostaglandins and other oxygenated derivatives. The role cytosol proteins play in regulating unsaturated fatty acid biosynthesis will be defined. Rates of reactions for the biosynthesis of acids derived from linolenate will be compared with rates previously obtained for acid derived from linolenate in order to further define whether reaction rates are useful predictors of fatty acid availability for complex lipid biosynthesis and thus also for prostaglandin synthesis. Hepatocytes prepared from chow fed as well as from rats maintained on defined diets will be used as a model to determine whether unsaturated fatty acid and phospholipid biosynthesis are coupled metabolic processes. Specific studies will be carried out with acids within a metabolic sequence to define why given acids are selectively incorporated into lipids. Similar experiments will be carried out using unsaturated acids from different metabolic families to define what type of metabolic regulation operates in vivo thus resulting in the incorporation of specific acids into complex lipids. Unsaturated fatty acids are one of the precursors for complex lipid biosynthesis and the resulting lipids are the reservoir for unsaturated fatty acids used to synthesize prostaglandin. Prostaglandins derived from different unsaturated acids frequently have unique and sometimes opposing biological properties. The immediate objective of these studies is to define the factors which regulate lipid unsaturated fatty acid composition. The ultimate objective would be to control lipid unsaturated fatty acid composition and thus provide the unsaturated fatty acid profile requied for the production of desired prostaglandins.